Device for producing a visual display of the transverse tension profile of a moving steel strip

ABSTRACT

A traversing mechanism, carrying a transducer and two proximity detectors, is continuously scanned transversely of a moving strip and produces a signal which is converted into a visual display indicative of the longitudinal tension in the strip.

United States Patent 1191 Fetner et al.

[ DEVICE FOR PRODUCING A VISUAL DISPLAY-OF THE TRANSVERSE TENSION PROFILE OF A MOVING STEEL STRIP [75] Inventors: Martin J. Fetner; Glenn L.

Hunsicker, both of Allentown, Pa.

[73] Assignee: Bethlehem Steel Corporation,

Bethlehem, Pa.

22 Filed: June 1, 1973 [21] Appl. No.: 365,950

[52] US. Cl. 73/143, 73/159, 324/34 ST [51] Int. Cl. G01] 5/10 [58] Field of Search 73/143, 159, DlG. 2;

324/34 ST, 34 TK [56] References Cited UNlTED STATES PATENTS 111] 3,826,132 1451 July 30, 1974 3,553,570 l/l97l Skubiak et a1 324/37 3,603,874 9/1971 Posey 324/40 FOREIGN PATENTS OR APPLlCATlONS 1,160,124 7/1969 Great Britain 73/DlG. 2

OTHER PUBLlCATlONS J. R. Dahm, On1ine Sensor Gages Shape of Strip Steel, Instrumentation Technology, May, 1970, pp. 54-59.

Primary Examiner-Charles A. Ruehl Attorney, Agent, orFirm-Joseph J. OKeefe; John 1. lverson; Robert M. Jones ABSTRACT A traversing mechanism, carrying a transducer and two proximity detectors, is continuously scanned transversely of a moving strip and produces a signal which is converted into a visual display indicative of the longitudinal tension in the strip.

3,308,658 3/1967 Bryan"; 73/159 3,474,668 10/1969 Mangan 73/159 4 Claims, 6 Drawing Figures 4c SIGNAL rem/some AMPL/I'l/fl flMPL/F/'k. zmo' SOURCE pawl/44m: su /eets's/ozv SIG/VAL cum/r SAMPL S/GIVAL 2V All/0 #OM 1 Z-EX/S x-aws o l ear/w 1.06/6 me //o //4 m4 as f I aye/444702 066 I AWLITUD! SET-Pdl/VT VOLT/76E aerecraxz anneal/Mme camp/mama CL 4MP ///3 0e LOG/C as we I 2 I 0651 MPL/TUFE SEFPoM/r van/1a: flint-T012. pemwuraz COMPAUTOR CLAMP 0c FOIZ'NTMETER SUPPLY 01V TMVEPS/NG MCAMNISM PATENTEU Jul-301974 3. 825,132

SHEET 3 OF 4 I 4 DEVICE FOR PRODUCING A VISUAL DISPLAY OF THE TRANSVERSE TENSION PROFILE OF A MOVING STEEL STRIP BACKGROUND OF THE INVENTION This invention relates to indicating devices, and more particularly to devices for producing a visual display of the transverse tension profile of a moving strip of ferromagnetic material, e.g. low carbon steel strip.

The production of steel strip having a high degree of flatness is of major concern to the steel industry, particularly in the case of extra-thin strips such as the socalled double-reduced in which strip thicknesses of the order of 0.006-0.010 inches are produced. It has been found that differences in elongation as small as 0.01 percent across the width of the strip result in unsatisfactory shape. Such differences in elongation are not visually observable while the strip is being rolled due to the fact that the strip is under high tension.

Inasmuch as elongation is proportional to tension, devices have been built to detect the tension across the width of a strip. This tension profile can then be used to alter the mill parameters, e.g. interstand cooling, to minimize differences in elongation across the width of the strip.

It is well known that when tension is applied to a ferromagnetic material such as low carbon steel strip, the magnetic permeability thereof changes in the direction of the applied stress. This-principle has been utilized in prior tension profile gauges by providing transducers which are magnetically coupled to the steel strip being gauged. Changes in the permeability of the steel affect the output of the transducers and indicate changes in tension. Such gauges typically comprise a plurality of transducers disposed in fixed relation transversely of the strip, each transducer or group thereof sensing the tension in one transverse section of the strip. These gauges have required, in addition to a large amount of expensive transducers, critical calibrating and balancing circuits due to inherent differences in transducer characteristics. In addition, indication of shape close to the edges of the strip and shape indication for strips of varying widths have not been satisfactory.

It has been suggested that a device having a single transducer be mechanically scanned across the strip. One of the problems in providing such a device has been that, as the transducer passes from a position directly beneath the strip to a position on either side of the strip, i.e. when the transducer passes an edge of the strip, the extreme difference in magnetic permeability between air and steel causes extremely large induced voltages in the transducer which require significant amounts of time to dampen. This condition will reoccur when the transducer begins its next traverse across the strip in the opposite direction. These extremely large voltages have prevented presently available visual display devices from producing an accurate visual indication of the tension near the edges of the strip.

It is accordingly an object of this invention to provide means for producing a visual display of the transverse tension profile of a moving steel strip in which such large voltages are prevented from introducing inaccurate indications of the tension near the edges of the ducing such a visual display.

SUMMARY OF THE INVENTION An electromagnetic transducer, having a primary winding to which an alternating currentcarrier wave is supplied, and a secondary winding in which induced voltage signals are produced, is mounted on support means adapted to be driven transversely of the strip of ferromagnetic material the tension profile of which is to be visually displayed. The invention comprises providing means on the support means for producing a control signal when the transducer is approximately at each edge of the strip. Means is connected to the secondary windings for amplitude demodulating the signals induced therein. A visual display unit having a sweeping independent x-axis, a dependent variable yaxis, and a z-axis is provided. A sample-and-hold circuit receives the amplitude-demodulated signal and supplies said signal to said dependent variable y-axis. Means controlled by the control signal is connected to the sample-and-hold circuit for switching off the z-axis and switching the circuit from the sample mode to the hold mode when the transducer is moving from a position directly beneath the strip to a position away from the strip, and for switching on the z-axis and switching the circuit from the hold mode to the sample mode when the transducer is moving from a position away from the strip to a position directly beneath the strip. Thus, the extremely large voltages induced in the secondary windings are not fed to the visual display unit.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation view of a strip traversing apparatus.

FIG. 2 is a sectional view through the lines 2-2 of FIG. 1.

FIG. 3 is a plan view of the apparatus shown in FIG. 1.

FIG. 4 is a diagrammatic view of the hydraulic system which controls the traversing apparatus of FIGS. 1-3.

FIG. 5 is a diagrammatic view of a transducer adapted to traverse strip.

FIG. 6 is a block diagram of the circuits of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIGS. 1, 2 and 3, a traversing apparatus 10 is disposed intermediate tension rolls 12 and 14 over which a strip 16 is passed under considerable tension. The apparatus 10 broadly comprises a supporting framework 18, disposed transversely to the direction of V strip movement, upon which a traversing transducer assembly 20 is driven transversely of the strip 16. A fiberglass window 21 in the framework 18 protects the transducer assembly 20 from dirt, oil, etc.

Referring more particularly to FIG. 1, the transducer assembly 20 is shown as comprising a transducer housing 22 secured to an upper plate 24. The plate 24 is secured, by'means of leveling screws 26, to a saddle 28. As shown in FIG. 2, the saddle 28 is provided with a key 30 adapted to slide along the way 32 in the base plate 34.

The saddle 28 is connected to a cable 36 which passes around pulleys 38 and 40 rotatably mounted on opposite sides of the framework 18. Pulley 38 is a drive pulley, and is provided with a pinion gear 42 which engages a spur gear 44 adapted to drive the wiper arm of a potentiometer 46. The cable 36 makes several turns around the drive pulley 38 and passes into one end of a double-acting hydraulic cylinder 48. Similarly, the cable 36 passes around the idle pulley 40 and passes into the other end of the hydraulic cylinder 48. Mounted on the base plate 34 are limit switches 50 and 52 adapted to be actuated by a trip plate 54, secured to the side of the saddle 28, to control the direction of fluid flow in the hydraulic cylinder 48.

The system for controlling the fluid flow in the cylinder 48 is shown diagrammatically in FIG. 4, and comprises oil reservoir tanks 58 and 60 connected through solenoid-operated flow valves 66 and 68, respectively, to opposite ends of the cylinder 48. The valves 66 and 68 are adapted to be actuated by a switch (not shown), and function to block the flow of oil into and out of the cylinders 58 and 60, thus stopping traversal of the transducing assembly 20 and permitting inspection of a fixed area of the strip passing thereover. The flow of oil into and out of the tanks 58 and 60 is controlled by a compressed air system comprising a four-way solenoid valve 70, an air inlet source 72, and an air exhaust line 74. The valve 70 is adapted to switch the air supply lines to the tanks 58 and 60 from the exhaust state to the input state, and vice versa, in response to actuation by the limit switches 50 and 52. This switching action reverses the direction of the force on the piston within the hydraulic cylinder 48, and causes the saddle 28 to be continuously reciprocated transversely of the strip 16. Preferably, the period of reciprocation is about 4 to seconds. I

The transducer assembly preferably comprises a four-pole transducer 75, shown diagrammatically in FIG. 5. The core 76 comprises stacks of laminated sheet steel Us provided with notches 77 at their bases whereby they may be joined so that all the laminations of one stack make direct contact with all the laminations in the other stack. The primary windings 78 are on one stack, while the secondary windings 80 are on the other stack. The transducer 75 is disposed in the housing 22 such that each primary has one secondary aligned with it transversely of the strip and the other secondary aligned with it longitudinally of the strip. As a result of this arrangement, the effects of parameters other than the tension in the strip are minimized.

Also disposed in the transducer assembly 20 are two proximity detectors comprising inductors 86 and 88 disposed approximately at the outer edges of the transducer 75. The function of said proximity detectors will become clear from the description of the electrical circuits of the invention which follows.

The electrical supply lines for the transducer 75 and the inductors 86 and 88 are encased in a tubular casing 89 and hang loosely from the transducer assembly 20 during its traversals across the strip 16. The framework 18 is provided with a guide bar 91 for limiting the movement of the casing 89 as it hangs between the transducer assembly 20 and a junction box 93.

As shown in FIG. 6, a low frequency, e.g. 950 Hz. signal source 90 is provided for supplying an alternating current carrier wave to the primary windings 78 of the transducer 75. The secondary windings 80 of the transducer 75 have'voltage signals induced therein which are amplitude modulated by transverse variations in the tension of the strip. These "signals are supplied to an amplitude demodulator 92 which removes the 950 Hz carrier wave therefrom. The demodulated wave, which represents the tension profile, is then amplified and filtered in an amplifier 94, preferably passed through a zero suppression circuit 96 to provide a dc. bias to the signal, and supplied to a sample-and-hold circuit 98. The sample-and-hold circuit 98 provides this signal to the dependent variable y-axis of visual display means, e.g. an image storage tube 100.

The independent variable, or x-axis, of the image storage tube 100 is connected to the potentiometer 46, which in turn is connected to a source of do. 102. As the saddle 28 traverses the strip 16, the potentiometer 46 causes the beam, or z-axis, of the image storage tube 100 to sweep across the face of the tube along the xaxis with its position and rate of travel proportional to the position and rate of travel of the saddle 28.

Referring now to the proximity detector circuit, an

oscillator 104 continuously supplies a signal, e.g. 50

kHz, to the inductors 86 and 88. When the magnetic circuit of either inductor changes suddenly, e.g. when the transducer assembly 20 moves from a position directly beneath the. strip 10 to a position away from the strip 16, the amplitude of the signal which amplitude modulates the 50 kHz carrier wave increases greatly. The inductors 86 and 88 are connected to amplitude demodulators 106 and 108, respectively, which remove the carrier wave and supply the signals to level detectors 110 and 112, respectively. The outputs from the level detectors 110 and 112 are clamped by voltage clamps l 14 and 116, respectively, to prevent overloading of the circuit to which they are supplied, viz. NOR logic 118. The NOR logic 118 controls the z-axis of image storage tube 100 and the mode of the sampleand-hold circuit 98. When both inductors 86 and 88 are directly beneath the strip 16, there is a small output signal from both voltage clamps 114 and 116 which causes the NOR logic 1 18 to place the z-axis on and the sample-and-hold circuit 98 in the sample mode. However, when either or both of the inductors 86 and 88 are not directly beneath the strip, there is a large output signal from one or both of the voltage clamps 114 and 116 and the NOR logic 118 switches off the z-axis and switches the sample-and-hold 98 into the hold mode. After the transducer assembly 20 reverses direction, because of actuation of one of the limit switches 50 and 52, and reaches a position beneath the strip 16, the zaxis is switched back on and the sample-and-hold 98 is switched back into the sample mode. I

As a result of the foregoing circuits, the extremely large voltage indications which would otherwise appear on the image storage tube 100 when the transducer assembly 20 passes an edge of the strip are prevented.

We claim:

1. In a device for producing a visual display of the transverse tension profile of a moving steel strip, said device comprising an electromagnetic transducer having a primary winding to which an alternating current carrier wave is supplied and a secondary winding in which induced voltage signals are produced, support means for carrying said transducer, and means for driving said support means transversely of said strip, the improvement comprising:

a. means disposed on said support means for producing a control signal when said transducer is approximately at each edge of said strip;

b. means connected to said secondary windings for amplitude demodulating the signals induced therein;

c. a visual display unit having a sweeping independent x-axis, a dependent variable y-axis, and a zaxis;

d. a sample-and-hold circuit for receiving the amplitude-demodulated signal and supplying said signal to said dependent variable y-axis; and

e. means controlled by said control signal connected to said sample-and-hold circuit for switching off said z-axis and switching said circuit from the sample mode to the hold mode when said transducer is moving from a position directly beneath said strip to a position away from said strip, and for switching on said z-axis and switching said circuit from the hold mode to the sample mode when said transducer is moving from a position away from said strip to a position directly beneath said strip.

2. A device as recited in claim 1, in which means (a) comprises first and second inductors, each of said inductors being disposed approximately at the lateral extremes of said transducer.

3. A device as recited in claim 1, in which means is mechanically linked to said support means for controlling the lateral position of the sweeping independent axis of means (c).

4. Ina method of displaying the transverse tension profile of a moving steel strip on a visual display unit having a sweeping independent x-axis, a dependent variable y-axis, and'a z-axis, said method comprising reciprocating transversely of said strip an electromagnetic transducer having a primary winding to which an alternating current carrier wave is supplied and a secondary winding in which induced voltage signals are produced, the improvement comprising:

a. producing a control signal indicative of said transducer being approximately at an edge of said strip;

b. amplitude demodulating said induced signals and beneath said strip. 

1. In a device for producing a visual display of the transverse tension profile of a moving steel strip, said device comprising an electromagnetic transducer having a primary winding to which an alternating current carrier wave is supplied and a secondary winding in which induced voltage signals are produced, support means for carrying said transducer, and means for driving said support means transversely of said strip, the improvement comprising: a. means disposed on said support means for producing a control signal when said transducer is approximately at each edge of said strip; b. means connected to said secondary windings for amplitude demodulating the signals induced therein; c. a visual display unit having a sweeping independent x-axis, a dependent variable y-axis, and a z-axis; d. a sample-and-hold circuit for receiving the amplitudedemodulated signal and supplying said signal to said dependent variable y-axis; and e. means controlled by said control signal connected to said sample-and-hold circuit for switching off said z-axis and switching said circuit from the sample mode to the hold mode when said transducer is moving from a position directly beneath said strip to a position away from said strip, and for switching on said z-axis and switching said circuit from the hold mode to the sample mode when said transducer is moving from a position away from said strip to a position directly beneath said strip.
 2. A device as recited in claim 1, in which means (a) comprises first and second inductors, each of said inductors being disposed approximately at the lateral extremes of said transducer.
 3. A device as recited in claim 1, in which means is mechanically linked to said support means for controlling the lateral position of the sweeping independent axis of means (c).
 4. In a method of displaying the transverse tension profile of a moving steel strip on a visual display unit having a sweeping independent x-axis, a dependent variable y-axis, and a z-axis, said method comprising reciProcating transversely of said strip an electromagnetic transducer having a primary winding to which an alternating current carrier wave is supplied and a secondary winding in which induced voltage signals are produced, the improvement comprising: a. producing a control signal indicative of said transducer being approximately at an edge of said strip; b. amplitude demodulating said induced signals and supplying the demodulated signals through a sample-and-hold circuit to said dependent variable y-axis; and c. in response to said control signal, switching off said z-axis and switching said sample-and-hold circuit from the sample mode to the hold mode when said transducer is moving from a position directly beneath said strip to a position away from said strip, and switching on said z-axis and switching said sample-and-hold circuit from the hold mode to the sample mode when said transducer is moving from a position away from said strip to a position directly beneath said strip. 